Here's how to calculate the mass of 0.139 moles of copper:

1. Find the molar mass of copper:

* The molar mass of copper (Cu) is 63.546 g/mol. This means one mole of copper weighs 63.546 grams.

2. Use the formula:

* mass = moles * molar mass

3. Plug in the values:

* mass = 0.139 moles * 63.546 g/mol

4. Calculate the mass:

* mass ≈ 8.84 grams

Therefore, the mass of 0.139 moles of copper is approximately 8.84 grams.